Glaucoma is a disease which causes a characteristic optic nerve cupping and an impairment in a visual field by retinal ganglion cell death. An elevation in an intraocular pressure is considered to be a major cause for the nerve cupping and the impairment in the visual field in glaucoma. On the other hand, there is also glaucoma in which an intraocular pressure is held within a normal range in statistical calculation, and even in this case, it is considered that glaucoma develops because the intraocular pressure is at a sufficiently high level for causing the impairment in a visual field for an individual.
The basic treatment for glaucoma is to maintain an intraocular pressure at a low level, and it is necessary to consider the causes for a high intraocular pressure in order to maintain a low intraocular pressure. Therefore, in the diagnosis of glaucoma, it is important to classify the types of glaucoma in accordance with the levels of intraocular pressures and causes therefor. As the causes for an elevation in an intraocular pressure, the presence or absence of closure of angle which is a major drainage pathway for an aqueous humor filling an eye is important. From these viewpoints, the primary glaucoma is roughly classified into the two groups of closed-angle glaucoma accompanying angle closure and open-angle glaucoma without accompanying angle closure. Among them, the open-angle glaucoma is classified into open-angle glaucoma, in a narrow sense, accompanying an elevation in an intraocular pressure, i.e. primary open-angle glaucoma, and normal tension glaucoma in which an intraocular pressure is held within a normal range.
It is known from old times that glaucoma is associated with inheritance. It is reported that 5 to 50% of individuals with open-angle glaucoma have a family history, and it is generally understood that 20 to 25% of individuals have hereditary causes. Based on these reports, studies on a search for a gene responsible for glaucoma are performed. As a result, it is reported that a mutation in myocilin (MYOC) gene is associated with open-angle glaucoma (See Patent Publication: 1), and that a mutation in optineurin gene (OPTN) is associated with normal tension glaucoma (See Non-Patent Publication: 1). However, all the genetic causes of glaucoma cannot be explained only by these genes, and the presence of unknown glaucoma-related genes is expected.
On the other hand, a single nucleotide polymorphism means that a substitution mutation in which a single base is changed into another base is found in base sequences of the genome of an individual, and the mutation exists in a certain frequency, generally a frequency of about 1% or more, in the population of an organism species. A single nucleotide polymorphism exists at intron or exon on genes, or any of the regions of the genome other than these.    Patent Publication 1: Japanese Patent-Laid Open No. 2002-306165    Non Patent Publication 1: Rezaie T and eleven others, Science, 2002, 295(5557), 1077-1079.